1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method. In particular, the present invention relates to an image processing apparatus and an image processing method capable of determining noise in image data obtained by moving a document with respect to a reading portion.
2. Description of the Related Art
There is conventionally known a technique so called “sheet through type (moving document scanning type) reading” incorporated into an image reading apparatus used in an MFP (Multi Function Peripheral), a digital copying machine, a facsimile, and the like. This technique allows an image to be read by moving a document with respect to a stationary reading portion of the image reading apparatus, instead of moving a reading portion with respect to a document.
Thus, if a foreign material such as dirt, dust, paper dust, or a flaw (hereinafter collectively called “dirt”) is on a reading position, the reading portion will always read the dirt while the document is being moved, unless the dirt moves to a position other than the reading position. Therefore, light reflected from an image of the document at a position corresponding to the position of the dirt does not reach the reading portion, causing a black line (image noise) extending on a read image and an output image in a sub scanning direction.
Consequently, it is contemplated to remove such dirt by cleaning a platen regularly. However, it has been difficult to always keep the platen clean, without any dirt.
In view of such a problem, Japanese Laid-Open Patent Publication No. 2002-185720 discloses a technique to see the continuity of read image data to detect a white or black line.
Japanese Laid-Open Patent Publication No. 2002-185704 discloses a technique to detect an irregular pixel from read image data and limit an effective reading position for a document depending on the position of the irregular pixel. In this technique, the continuity, position, and line width of the image data is detected for the detection of an irregular image.
Japanese Laid-Open Patent Publication No. 2002-271631 discloses an image reading apparatus including first reading means to read color image data and second reading means located offset from the first reading means in a sub scanning direction to read monochrome image data, which detects noise based on a comparison result of density values read by the first and the second reading means, and on a result of edge detection in the image data read by the first reading means.